1. Field of the invention
The present invention relates to vehicular electric machines each equipped with a rectifier and, more particularly, a vehicular electric rotary machine of a heat pipe cooling type for cooling a rectifier using a heat pipe.
2. Description of the Related Art
In the related art, it has been a common practice for a rectifier of a vehicular alternator to be integrally incorporated into the alternator having an armature winding and a field winding. Such an all-in-one vehicular alternator with the rectifier of the related art is described below.
The rectifier usually includes a positive-electrode heat radiation fin doubling as a positive-electrode output terminal, three-phase diodes (rectifying elements) fixedly secured onto the positive-electrode heat radiation fin on an upper arm side, and diodes (rectifying elements) fixedly secured onto the negative-electrode heat radiation fin on an upper arm side and forming a full-wave rectifying circuit together with the diodes on the upper arm side. In general, the positive-electrode heat radiation fin is usually formed on a rear end wall of an alternator housing (on a side opposite to a pulley) in a substantially radial direction and the negative-electrode heat radiation fin is placed in a position parallel to the positive-electrode heat radiation fin or in an overlapped status. The diode usually includes a metallic outer periphery processed in knurling and the heat radiation fin has a diode insertion through-bore. The alternator includes a centrifugal fan fixedly secured to a rotor of the alternator for creating a cooling wind that is drawn from intake passages formed at a rear end wall of the alternator housing into the alternator housing, that is, into a frame while contacting the positive-side rectifiers and negative electrode rectifiers. Then, upon cooling the inside of the alternator housing, the cooling wind is exhausted from exhaust passages formed on an outer circumferential periphery of the alternator housing.
With the vehicular alternator of such a kind, a strong need arises for the alternator to provide an increased power output. As a result, a related art has a structure to allow the rectifier to be cooled with a cooling wind prior to flowing into the alternator housing with the resultant occurrence of a probability in which operating temperatures of the diodes exceed an allowable level.
To address such an issue, a proposal has heretofore been made in the related art to provide a vehicular electric rotary machine of a heat pipe cooling type wherein an external heat radiation mechanism is disposed on a circumferential periphery of the alternator housing at an external radiated area to allow the external heat radiation mechanism to be thermally connected to the frame at an area close proximity to the rectifier for causing a drop in temperatures of the diodes as disclosed in U.S. Pat. No. 4,295,067.
Further, another proposal has been made in the art to provide a vehicular electric rotary machine of a heat pipe cooling type wherein an external heat source such as a radiator is thermally connected to an alternator housing, that is, a frame via a heat pipe for thereby cooling the alternator housing as disclosed in Japanese Patent Provisional Publication No. 7-170695.
However, with the vehicular electric rotary machine of the heat pipe cooling type disclosed in the first related art set forth above, upon absorbing heat developed in the rectifier, fluid in the heat pipe needs to be cooled using an external cooling fin structural body of a large size located outside the alternator housing. Also, the external cooling fin structural body needs to additionally incorporate a ventilation mechanism. This results in a large size in construction and complicated in structure.
Similarly, with the vehicular electric rotary machine of the heat pipe cooling type disclosed in the second related art set forth above, due to a specific structure wherein heat developed in fluid in the heat pipe upon absorbing heat developed in the alternator housing is dissipated using the external heat radiator (radiator in normal practice), the heat pipe inherently has an extremely elongated length with the resultant difficulty in locating the heat pipe within a compact space inside the an engine room. During replacement of an old vehicular alternator with new one or demounting of the vehicular alternator from the engine room for maintenance, the external heat radiation device (radiator) needs to be separated from the heat pipe and, subsequently, the both component parts are assembled again causing troublesome labor work.